Process for suppression of hydrogenolysis and C5+ liquid yield loss in a cyclic reforming unit

Abstract

A process for reforming naphtha, with hydrogen, in a cyclic reforming unit which contains a plurality of catalyst-containing on-stream reactors in series, and a catalyst-containing swing reactor manifolded therewith which can be periodically placed in series and substituted for an on-stream reactor while the latter is removed from series for regeneration and reactivation of the catalyst contained therein. In the process, the ability of a catalyst to operate in a hydrogenolysis mode and effect sulfur release can be effectively suppressed after the freshly prepared catalyst has been regenerated, and reactivated several times, generally about five times or more, by the addition thereto of sufficient sulfur to maintain an equilibrium amount of sulfur on the catalyst, preferably a maximum of about 0.01 weight percent sulfur. Preferably, a modified catalyst presulfiding regimen is imposed wherein the amount of sulfur added to a fresh catalyst is progressively, and preferably proportionately reduced from one regeneration, reactivation sequence to the next such that, on and after about the fifth regeneration, and reactivation of the catalyst a maximum of about 0.01 weight percent sulfur is added to the catalyst. In a preferred mode of operation, the catalyst of the lead reactors of the series is not directly sulfided, but indirectly sulfided by sulfur added to, and released by the tail reactor, or reactors. An on-stream water wave displaces sulfur from the sulfided catalyst of the tail reactor, or reactors, as it is returned to service, and a water wave from the catalyst of each reactor redistributes sulfur to undersulfided catalysts of other reactors in the form of hydrogen sulfide released to and carried by the recycle gas.

Having described the invention what is claimed is: 
     
       1. In a process for reforming, with hydrogen, a naphtha in a cyclic reforming unit which contains a plurality of catalyst-containing on-stream reactors connected in series, and a catalyst-containing swing reactor which, due to an arrangement of process piping and valves comprising headers, can be substituted for any one of the on-stream reactors while the latter is off-stream for regeneration and reactivation of the catalyst, the hydrogen and naphtha feed flowing from one reactor of the series to another to contact the catalyst contained therein at reforming conditions, the improvement comprising adding a maximum of about 0.01 percent sulfur, based on the total weight of the catalyst, to the catalyst of a reactor after the freshly prepared catalyst has been regenerated and reactivated about five times, or more.   
     
     
       2. The process of claim 1 wherein after about the fifth regeneration/reactivation sequence the catalysts of the lead reactors of the series are no longer directly sulfided, but only the catalysts of the tail reactors are directly sulfided. 
     
     
       3. The process of claim 1 wherein the first reactor of the series is left unsulfided after about the fifth regeneration/reactivation sequence, and other reactors of the series are directly sulfided. 
     
     
       4. The process of claim 1 wherein the unit contains at least three on-stream reactors in series, the catalysts of the first two reactors of the series are left unsulfided after about the fifth regeneration/reactivation sequence, and other reactors of the series are directly sulfided. 
     
     
       5. The process of claim 1 wherein the unit contains at least four on-stream reactors in series, the first three reactors of the series are left unsulfided after about the fifth regeneration/reactivation sequence, and other reactors of the series are directly sulfided. 
     
     
       6. The process of claim 1 wherein the unit contains at least three on-stream reactors in series, at least the first three reactors of the series are left unsulfided after about the fifth regeneration/reactivation sequence, the last reactor of the series is substituted by a swing reactor, and only the catalyst of the swing reactor is directly sulfided prior to the substitution. 
     
     
       7. The process of claim 1 wherein the hydrogen gas from the last reactor of the series is dried to remove moisture, and recycle hydrogen containing less than about 50 parts of water, per million parts of hydrogen, is circulated within the unit. 
     
     
       8. The process of claim 1 wherein a series of four on stream reactors are identified, for convenience, as A, B, C, D, respectively, and the swing reactor is identified, for convenience as S, the improvement wherein after about the fifth regeneration/reactivation sequence the catalysts of the lead reactors are no longer directly sulfided, but only the tail reactors are directly sulfided. 
     
     
       9. The process of claim 8 wherein Reactor A is left unsulfided after about the fifth regeneration/reactivation sequence, and Reactors B, C and D, and Reactor S when substituted for any of Reactors B, C and D, are directly sulfided. 
     
     
       10. The process of claim 8 wherein the catalysts of Reactors A and B are left unsulfided after about the fifth regeneration/reactivation sequence, and Reactors C and D, and Reactor S when substituted for Reactors C and D, are directly sulfided. 
     
     
       11. The process of claim 8 wherein Reactors A, B and C are left unsulfided after about the fifth regeneration/reactivation sequence, and only Reactor D, and Reactor S when substituted for Reactor D, is sulfided. 
     
     
       12. The process of claim 8 wherein Reactors A, B and C are left unsulfided after about the fifth regeneration/reactivation sequence, Reactor D is substituted by swing Reactor S, and only the catalyst of Reactor S is directly sulfided. 
     
     
       13. The process of claim 8 wherein the hydrogen gas from the last reactor of the series is dried to remove moisture, and recycle hydrogen containing less than about 50 parts of water, per million parts of hydrogen, is circulated within the unit. 
     
     
       14. The process of claim 1 wherein sulfur is added to the catalysts during about the first five catalyst regeneration/reactivation sequences, the sulfur added to the catalyst being progressively reduced between the first catalyst regeneration/reactivation sequence and about the fifth at which time the sulfided catalyst contains a maximum of about 0.01 percent sulfur. 
     
     
       15. The process of claim 1 wherein sulfur is added to the catalysts during about the first five catalyst regeneration/reactivation sequences, the sulfur added to the catalyst being progressively reduced between the first catalyst regeneration/reactivation sequence and abut the fifth at which time the sulfided catalyst contains a maximum of about 0.01 percent sulfur, and thereafter sulfur is directly added only to a tail reactor, or to the swing reactor when it occupies the position of a tail reactor which has been removed for regeneration and reactivation of the catalyst contained therein. 
     
     
       16. The process of claim 1 wherein the catalysts are platinum catalysts promoted with a hydrogenation-dehydrogenation component, or components, which increase the rate of hydrogenolysis as contrasted with an unpromoted platinum catalyst. 
     
     
       17. The process of claim 16 wherein the platinum catalyst is promoted with rhenium. 
     
     
       18. In a process for reforming, with hydrogen, a naphtha in a cyclic reforming unit which contains a plurality of catalyst-containing on-stream reactors connected in series, and a catalyst-containing swing reactor which, due to an arrangement of process piping and values comprising headers, can be substituted for any one of the on-stream reactors while the latter is off-stream from regeneration and reactivation of the catalyst, the catalyst is a platinum catalyst promoted with a hydrogenation-dehydrogenation component, or components, which increase the rate of hydrogenolysis as contrasted with an unpromoted platinum catalyst, the hydrogen and naphtha feed flows from one reactor of the series to another to contact the catalyst contained therein at reforming conditions, the improvement comprising adding a maximum of about 0.01 percent sulfur to the catalyst of a reactor after about the fifth sequence of regeneration and reactivation of the freshly prepared catalyst, returning said reactor to the position occupied by the last reactor of the series and placing said reactor on-stream, drying the off gas from said reactor to remove water so that the moisture level of the gas recycled through the unit contains below about 50 ppm water.   
     
     
       19. The process of claim 18 wherein the platinum catalyst is promoted with rhenium. 
     
     
       20. The process of claim 18 wherein a maximum of about 0.001 percent to about 0.005 percent sulfur is added to the catalyst after about the fifth sequence of regeneration and reactivation. 
     
     
       21. The process of claim 18 wherein the moisture level of the gas recycled through the unit contains below about 20 ppm water. 
     
     
       22. The process of claim 18 wherein sulfur is added to the catalysts during about the first five catalyst regeneration/reactivation sequences, the sulfur added to the catalyst being progressively reduced between the first catalyst regeneration/reactivation sequence and about the fifth at which time the sulfided catalyst contains an equilibrium amount of sulfur, and thereafter a maximum of about 0.005 percent sulfur is directly added only to a tail reactor, or to the swing reactor when is occupies the position of a tail reactor which has been removed for regeneration and reactivation of the catalyst contained therein. 
     
     
       23. The process of claim 22 wherein a series of four on-stream reactors are employed, identified for convenience, as A, B, C, D, respectively, and the swing reactor is identified, for convenience as S, the improvement wherein after about the fifth regeneration/reactivation sequence the catalysts of Reactors A, B and C are no longer directly sulfided, but only the catalyst of Reactor D, and Reactor S when substituted for Reactor D, is directly sulfided.